Prior art workers have devised numerous types of conveyors and stackers utilizing spiral elements or rotating screws having helical threads. For example, U.S. Pat. No. 2,556,214, issued in the name of R. K. Pottle on June 12, 1951, teaches a machine for counting, stacking and packing sheet can ends. The machine employs a rotating cut-off knife, having a spiral groove to separate a predetermined number of can ends from a magazine thereof, so that they can be ultimately fed to cylindrical packing tubes. U.S. Pat. No. 2,954,133, issued to J. C. H. Geisow on Sept. 29, 1960, describes a reversible stacking and unstacking mechanism. The mechanism employs a pair of mirror image cams having spiral edge portions for separating and feeding flat articles.
Commonly-owned co-pending application Ser. No. 428,319, in the names of Howard N. Watrous, Walter Cash, Jr. and Weldon R. Dixon, filed Sept. 29, 1982, and entitled "POSITIVE CONTROL STACKER", teaches a high speed stacker for rigid and semi-rigid sheet or pad-like products utilizing one or more cooperating pairs of screws having properly configured spiral or helical threads. The screw pairs are utilized to form product stacks of specific count, with the products of each stack being aligned. One or more pairs of continuously rotating single-thread screws can be utilized in conjunction with the one or more pairs of stacker screws either to simply convey the stacks formed by the stacker screws, or to accumulate and convey the stacker screw stacks, depending upon the rotational speed of the single-thread screws, relative to the stacker screws.
Numerous other types of stacking devices have been developed. These devices depend on intermittent motion to identify and segregate product stacks. Stackers of this general type are inherently slow and are usually characterized by complex construction.
The present invention is based upon the discovery that numerous advantages can be achieved by employing a simple spiral assembly as a stacking element, the spiral assembly preferably being vertically oriented with its axis of rotation horizontally oriented and being rotated at a constant speed about its axis. The spiral assembly comprises a single spiral element or a pair of spaced mirror image spiral elements having an exterior leading edge, an interior trailing edge, and an exterior product supporting surface. The leading edge of the spiral assembly passes through a stack-building area and individual products are deposited on the exterior surface of the spiral element, one on top of the other. Means are provided to maintain the products stationary within the stack-building area as the exterior surface of the spiral assembly passes therethrough. At the end of a complete revolution of the spiral assembly, the leading edge thereof again passes through the stack building area to begin a new stack and segregate the new stack from the previously accumulated stack. Meanwhile, the trailing edge of the spiral assembly slips out from under the previously accumulated product stack, depositing it on an outfeed device passing through the spiral assembly.
The spiral stacker of the present invention forms product stacks of specific count. The spiral assembly, its supports, and the means imparting rotating to it are the only moving parts of the device.
The spiral stacker of the present invention is characterized by unusually simple mechanical construction. Since the spiral stacker utilizes continuous rotary motion, it has an inherently higher speed potential than devices depending upon intermittent motion to identify and segregate a product stack. The device may be used for a wide range of products ranging from thin, flat products to thick, semi-flat products of the same general size and shape. While not so limited, the high proportion of peripheral motion to stack motion renders the spiral stacker ideally suited for thin products.